Powered snowthrowers are well known and are generally either single stage or two stage. A typical single stage snowthrower is illustrated in U.S. Pat. No. 3,359,661 to Speiser. Such a snowthrower includes a housing which is generally open in front having spaced side walls connected by a rear wall that includes an arcuate lower portion. A snowthrowing impeller is rotatably journalled between the side walls to sit in front of the lower portion of the rear wall. The impeller includes two radially extending paddles, which are flexible for picking up and throwing snow. The upper portion of the rear wall of the housing includes a plurality of transversely spaced snow deflecting vanes. As the impeller rotates, the paddles pick up snow and carry the snow against the arcuate lower portion of the rear wall. When the paddles diverge from the arcuate lower portion at the tangent point where the upper portion of the rear wall begins, the forces acting on the snow cause it to be released from the paddles and to be thrown upwardly and outwardly generally along the upper portion of the rear wall. Depending upon the orientation of the vanes, the snow is thrown either forwardly or to the left or right.
The single stage snowthrower just described is so named because it utilizes only one powered implement, namely the impeller, for both picking up and throwing the snow outwardly away from the snowthrower. This may be contrasted with two stage snowthrowers which utilize two separate means for consecutively handling the snow. In any conventional two stage, such as the 521 snowthrower manufactured and sold by The Toro Company of Minneapolis, Minn., there is again a housing having an open front portion. However, a snow gathering auger, rather than a paddle-type impeller, is journalled in the front portion. The auger has generally opposed left and right helical flights which gather snow and feed it inwardly toward the center of the housing. There is an opening at the center of the rear wall which connects the auger to a chamber situated rearwardly thereof. This chamber includes a second powered element, namely a high speed rotatable fan, which takes the snow gathered by the auger and throws it vertically upwardly through a stack. The top of the stack includes a rotatable chute that can be rotated by a gear and handle arrangement to face toward the front or to the left and right respectively.
Both types of snowthrowers have their own particular advantages and disadvantages. Single stage snowthrowers are generally lighter and less expensive than two stage snowthrowers, but they generally do not throw snow as far or control the direction of the thrown snow as well as do two stage snowthrowers. While two stage snowthrowers have the ability to direct the snow to a precise location, because of the rotatable chute on top of the stack, they lose some efficiency because of the different directions in which the snow is moved. The snow is first "chopped up" and moved inwardly by the auger, then moved rearwardly into the fan chamber, then thrown upwardly through the stack, and finally directed to the left, right or forwardly depending upon the direction of the chute. Snow can more easily clog in such a tortuous path. Moreover, the need for two separate snow contacting and moving elements, namely the auger and the fan, adds to the cost and complexity of the two stage.
There have been attempts in recent years to have what might be called a mid-model snowthrower or a cross between a single stage and a two stage. In such a snowthrower, as illustrated in U.S. Pat. No. 4,322,896 to Miyazawa, only a single, rotatable impeller is used which includes, however, opposed auger flights that feed snow to a central section that rotates on the same shaft as the auger flights. This central section, which is simply a flat and relatively short paddle, takes the inwardly moving snow from the augers and throws it up vertically through a stack and chute arrangement somewhat similar to that found in two stages. Such a snowthrower allegedly gives one the advantages of a two stage, more precise directional control for example, without sacrificing the advantages of a single stage, namely only one active snow throwing element.
While the above noted snowthrower has attempted to successfully combine both single stage and two stage technology, it exhibits some disadvantages. For one thing, Applicants have discovered that the auger sections often overfeed snow to the impeller section. In other words, at a normal forward walking speed for the operator of the snowthrower, the auger sections deliver snow to the impeller section generally faster than the impeller section can remove it from the housing by throwing it up the stack. This can contribute to clogging of the impeller section with snow which obviously is undesirable. Moreover, the relatively extended length of the auger sections and the high rotational speed thereof allow such sections to radially throw an appreciable amount of snow upwardly rather than augering it inwardly. Accordingly, even when the impeller section does not clog, a conconsiderable amount of snow is recirculated instead of being clearly thrown by this snowthrower. The physical manifestation of this is snow spit or dribbling which extends out forwardly from the auger sections of the impeller and which detracts from the aesthetic appearance of the snowthrower during operation and may also lessen how fast the snowthrower can be pushed forwardly.